Oh no sewer ratz... A giant woolly rat

The Bosavi woolly rat had no fear of humans when it was discovered. Photograph: Jonny Keeling/BBC

A lost world populated by fanged frogs, grunting fish and tiny bear-like creatures has been discovered in a remote volcanic crater on the Pacific island of Papua New Guinea.

'A giant woolly rat never before seen by science' Link to this audio A team of scientists from Britain, the United States and Papua New Guinea found more than 40 previously unidentified species when they climbed into the kilometre-deep crater of Mount Bosavi and explored a pristine jungle habitat teeming with life that has evolved in isolation since the volcano last erupted 200,000 years ago. In a remarkably rich haul from just five weeks of exploration, the biologists discovered 16 frogs which have never before been recorded by science, at least three new fish, a new bat and a giant rat, which may turn out to be the biggest in the world.

The discoveries are being seen as fresh evidence of the richness of the world's rainforests and the explorers hope their finds will add weight to calls for international action to prevent the demise of similar ecosystems. They said Papua New Guinea's rainforest is currently being destroyed at the rate of 3.5% a year.

"It was mind-blowing to be there and it is clearly time we pulled our finger out and decided these habitats are worth us saving," said Dr George McGavin who headed the expedition.

The team of biologists included experts from Oxford University, the London Zoo and the Smithsonian Institution and are believed to be the first scientists to enter the mountainous Bosavi crater. They were joined by members of the BBC Natural History Unit which filmed the expedition for a three-part documentary which starts tomorrow night.

They found the three-kilometre wide crater populated by spectacular birds of paradise and in the absence of big cats and monkeys, which are found in the remote jungles of the Amazon and Sumatra, the main predators are giant monitor lizards while kangaroos have evolved to live in trees. New species include a camouflaged gecko, a fanged frog and a fish called the Henamo grunter, named because it makes grunting noises from its swim bladder.

"These discoveries are really significant," said Steve Backshall, a climber and naturalist who became so friendly with the never-before seen Bosavi silky cuscus, a marsupial that lives up trees and feeds on fruits and leaves, that it sat on his shoulder.

"The world is getting an awful lot smaller and it is getting very hard to find places that are so far off the beaten track."